What is a Metal Oxide Varistor (MOV)?
A Metal Oxide Varistor (MOV) is an electronic component primarily used for overvoltage and surge protection. It is a non-linear, bidirectional voltage-dependent resistor that helps protect sensitive electronic circuits from sudden voltage spikes and transient surges.
Under normal operating voltage, an MOV has high resistance and allows only a very small leakage current. When a voltage surge occurs and the voltage rises above the MOV’s operating threshold, its resistance decreases sharply, allowing it to divert the surge current away from sensitive components.
This makes MOVs widely used in power supplies, electrical equipment, appliances, industrial electronics, surge protection devices and other AC/DC applications.
How Does an MOV Work?
The easiest way to understand an MOV is to think of it as a voltage-controlled safety valve.
During normal operation:
Normal Voltage → High MOV Resistance → Very Low Current
When a sudden surge occurs:
Voltage Surge → MOV Resistance Drops → Surge Current is Diverted → Circuit is Protected
An MOV has a non-linear current-voltage characteristic. Once the applied voltage reaches the MOV’s varistor voltage region, the current through the device increases significantly. The MOV therefore limits, or clamps, the voltage seen by the protected circuit.
Example
Imagine an electronic power supply connected to an AC mains line. A sudden transient caused by switching, lightning-related disturbances, or other events can produce a voltage spike.
Without appropriate surge protection, this spike may reach sensitive components such as:
- MOSFETs
- ICs
- Microcontrollers
- Rectifier diodes
- Power supplies
- Control circuits
An appropriately selected MOV can conduct the excess surge current and help limit the voltage reaching these components.
: What It Is, How It Works & Applications){kind=link}